1. Field of the Invention
The present invention relates to a fire extinguishing agent and a fire extinguisher, particularly, to a fire extinguishing agent that releases carbon dioxide and a fire extinguisher using this fire extinguishing agent.
2. Description of the Related Art
It was customary to use a fire extinguisher having a fire extinguishing agent housed therein for extinguishing a small fire. The known fire extinguishing agents include, for example, alkali hydrogencarbonates such as sodium hydrogencarbonate and potassium hydrogencarbonate. If put in the fire, these fire extinguishing agents generate carbon dioxide by the reaction denoted by formula (1) given below so as to lower the oxygen concentration and, thus, to exhibit a fire extinguishing function:2NaHCO3→CO2+H2O+Na2CO3  (1)
Also, the alkali ions exhibit high reactivity with OH radicals. Therefore, if the alkali hydrogencarbonate in the form of a fine powder is released into a flame together with the air stream, the alkali ions serve to suppress the chain reaction with the OH radicals within the flame so as to contribute to the fire extinguishing function.
On the other hand, improvement in the fire extinguishing efficiency per unit volume of the fire extinguishing agent is required in compliance with the demands for improvement in operability of the fire extinguisher or for reduction in space needed for installation. Also, it is stipulated in a ministerial ordinance specifying the technical standards of the fire extinguishing agents for the fire extinguisher, i.e., Ordinance No. 28 of the Ministry of Home Affairs dated Sep. 17, 1964, that the fire extinguishing agent should not be settled on the bottom within one hour when the fire extinguishing agent is uniformly sprayed on the water surface in order to permit the fire extinguishing agent to be capable of coping with both wood fires and oil fires.
Japanese Patent Disclosure (Kokai) No. 11-206910 discloses a fire extinguishing agent prepared by granulating, for example, an alkali hydrogencarbonate by using a hydrophilic binder such as carboxymethylcellulose or starch so as to increase the grain density of the fire extinguishing agent and, thus, to facilitate arrival of the fire extinguishing agent at a burning material. This document also teaches an idea of adding an auxiliary (water repellent) such as white carbon, organic silicone oil or metallic soap to the fire extinguishing agent so as to permit the fire extinguishing agent to exhibit water repellency.
However, in the fire extinguishing agent disclosed in the document quoted above, it is essential to apply heat treatment to the water repellent at about 150° C. What should be noted is that it is possible for the reaction denoted by formula (1) given above to take place during the heat treatment, which deteriorates the fire extinguishing agent.